Conventionally, pressure sensors of a diaphragm type for detecting a change in a pressure to be measured as a change in electrostatic capacitance have been broadly known. As one example of such a pressure sensor there is a known diaphragm-type sensor wherein a filter is placed on a connecting hole between a vacuum chamber and a diaphragm vacuum gauge, to prevent non-reacted substances, byproduct substances, particulates, and the like, from getting into a vacuum gauge from a vacuum chamber, to prevent these deposition components from adhering to and being deposited onto the pressure-sensitive diaphragm that structures the diaphragm sensor. (See, for example, Japanese Unexamined Patent Application Publication H10-153510 (Pages 2 through 3 and FIG. 1)).
While the diaphragm sensor of the structure described above can prevent the adhesion, to the pressure-sensitive diaphragm, of highly linear deposition components such as the non-reacted substances, byproduct substances, particulates, and the like, that are included in the medium to be measured, because it is necessary to direct the pressure to be measured to the pressure-sensitive diaphragm, it is impossible to completely exclude the deposition components through filtering.
When a portion of these deposition components in the medium to be measured is deposited onto the surface that contacts the pressure-sensitive diaphragm, the pressure sensor diaphragm flexes in one direction, producing zero-point shift (a movement of the zero point). That is, the deposits adhering to the pressure sensitive diaphragm produce internal stresses, such as compressive stresses or tensile stresses, after adhesion, depending on the component, disrupting the balance of forces in the direction of thickness of the pressure-sensitive diaphragm by pulling on or compressing also the side of the pressure-sensitive diaphragm that comes into contact with the medium to be measured. This causes the pressure-sensitive diaphragm flex to be convex on the side of the median to be measured, or on the side opposite therefrom.
It is impossible to cause the deposits, which will vary depending on the medium to be measured, and the materials of the pressure-sensitive diaphragms to always match each other, and, microscopically, the arrangements of the atoms in the deposited substances and in the pressure-sensitive diaphragms rarely match perfectly, and thus the deposited substances normally produce the compression or elongation described above. Given this, the flexure of the pressure-sensitive diaphragm becomes larger the greater the amount of the deposited substance that is deposited on the pressure-sensitive diaphragm.
In this electrostatic capacitive pressure sensor, a pressure difference is detected based on the electrostatic capacitance that changes depending on the flexure of the pressure-sensitive diaphragm, and thus the phenomenon described above gives rise to a zero point error, known as “zero point shift,” by detecting a signal indicating a pressure difference even in a state wherein there is no pressure difference across the pressure-sensitive diaphragm. Because of this, a problem is produced in that measurement errors will occur. Concomitant with this, a problem occurs in that this increases the frequency with which the pressure-sensitive diaphragm, that is, the diaphragm-type sensor, is changed, reducing the durability and increasing the cost thereof.
The object of the present invention is to provide an electrostatic capacitance pressure sensor wherein the zero point shift is reduced extremely through preventing the flexure of the pressure-sensitive diaphragm even when the medium being measured adheres to and is deposited on the pressure-sensitive diaphragm.